In a conventional individual section (I.S.) glass forming machine, there are provided a plurality of individually operable sections, each section having a blank mold station and a blow mold station. At a blank mold station, a molten glass gob is forced upwards by a plunger through a split neck mold and around the plunger. The plunger is withdrawn and a charge of air is forced into the depression left by the plunger, forming an inverted parison. A neckring mechanism holding the split neck mold rotates 180.degree., transferring the parison from the blank mold station to the blow mold station. In the process, the parison is inverted 180.degree. with the mouth of the now hanging parison being supported by the neck mold. A pair of blow mold halves next firmly grasps and holds the parison, allowing the neckring mechanism to separate the neck mold halves from the parison and rotate them back 180.degree. to the blank mold station to repeat the cycle. A more detailed description of an I.S. glass forming machine is provided in U.S. Pat. No. 2,702,444 issued to Rowe.
Conventional neckring mechanisms such as those disclosed in Rower and in U.S. Pat. No. 3,233,999 issued to Mumford and U.S. Pat. No. 3,024,571 issued to Abbott et al. include a horizontal shaft which is oscillated 180.degree. by a rack and pinion assembly. A pair of neckring holder arms are attached to cylinders which surround the shaft and which slide telescopically along the shaft between open (apart) and closed (together) positions. The cylinders are moved between the open and closed positions by piston assemblies which are coaxial with and integrally operable with the horizontal shaft. Both the horizontal shaft and the surrounding cylinders are splined for mutual engagement and rotation as a unit about the axis of the shaft.
The problems with these and similar types of neckring mechanisms are many. Pitch line misalignment of the cylinders is a recurring problem due to backlash between the cylinders and the shaft. Adjustment too tight causes increased wear which results in backlash and further misalignment of the neck molds. Adjustment too loose also results in backlash. Further, the splined shaft and splined cylinders are ineffective at sealing the pneumatic piston assemblies from air leakage which may result in the neck molds not opening completely. This causes increased wear, pneumatic inefficiency and overall poor performance of the neckring mechanism. Moreover, splined shafts and cylinders are expensive both to manufacture and to maintain.